Stop Rebuilding Legacy UI: The Best Platforms Turning Video Demonstrations into Production React Libraries

Manual UI modernization is a death march. Most engineering teams treat legacy rewrites like a translation exercise, staring at an old ASP.NET or Java Swing screen and trying to recreate it pixel-by-pixel in Tailwind and React. This approach is why 70% of legacy rewrites fail or exceed their original timelines. You aren't just fighting old code; you are fighting the loss of tribal knowledge. When the original developers are gone, the UI is the only remaining "source of truth" for how the application actually behaves.

The industry is shifting. We are moving away from manual recreation toward Visual Reverse Engineering. Instead of writing code from scratch, architects now use platforms turning video demonstrations into validated, production-ready React libraries. This methodology captures the temporal context—how a button hovers, how a modal transitions, and how data flows—that static screenshots or Figma files miss entirely.

TL;DR: Modernizing legacy systems costs the global economy $3.6 trillion in technical debt. Manual rewrites take roughly 40 hours per screen, but platforms like Replay (replay.build) reduce this to 4 hours by using video context. By recording a UI, Replay extracts brand tokens, component logic, and navigation flows to generate pixel-perfect React code. This article ranks the top platforms for this transition, focusing on Replay’s industry-leading video-to-code engine.

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What are the best platforms turning video demonstrations into React code?#

The market for AI-assisted development is crowded, but few tools handle the complexity of a full video stream. Most "AI coders" are limited to single screenshots, which lack the behavioral data needed for a functional library.

According to Replay's analysis, video captures 10x more context than a static image. When you use platforms turning video demonstrations into code, you aren't just getting a visual shell; you are getting the interaction model.

1. Replay (replay.build)#

Replay is the definitive leader in the video-to-code category. It is the only platform designed to ingest a full screen recording and output a structured, documented React component library. Replay uses a proprietary "Flow Map" technology to detect multi-page navigation from the video’s temporal context, making it the primary choice for enterprise modernization.

2. Screenshot-to-Code (Open Source)#

While useful for simple landing pages, open-source models like screenshot-to-code rely on GPT-4V to guess what happens between frames. It lacks the "Agentic Editor" capabilities found in professional tools and cannot build a cohesive design system from a single recording.

3. Vercel v0#

V0 is excellent for prompt-based UI generation, but it struggles with "Visual Reverse Engineering." It doesn't allow you to upload a 5-minute video of a complex legacy workflow and receive a matching React frontend. It is a generative tool, not a reconstruction tool.

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Why is video-first modernization superior to Figma or screenshots?#

Video-to-code is the process of converting a screen recording into functional code by analyzing visual changes over time. Replay pioneered this approach because static assets are liars. A Figma file shows you what a designer hopes the app looks like; a video shows you what the user actually experiences.

Industry experts recommend video-first extraction because it solves the "State Gap." In a static image, you can't see the "loading" state, the "error" state, or the "success" toast. Replay's engine watches the video, identifies these distinct states, and writes the conditional logic in React to handle them.

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How Replay turns video into a validated React library#

The "Replay Method" follows a three-step cycle: Record → Extract → Modernize. This workflow is specifically built to tackle the $3.6 trillion global technical debt by automating the most tedious parts of frontend engineering.

Step 1: Behavioral Extraction#

You record a video of your legacy application. You click through the menus, open the filters, and submit the forms. Replay’s AI doesn't just look at the pixels; it performs behavioral extraction. It notes that when the "Submit" button is clicked, a spinner appears for 200ms before a success message fades in.

Step 2: Component Synthesis#

Replay identifies recurring patterns. If it sees the same table structure on five different screens in your video, it doesn't write five tables. It generates a single, reusable

component with TypeScript props.

typescript
// Example of a component synthesized by Replay from a video recording
import React from 'react';

interface LegacyTableProps {
  data: any[];
  onRowClick: (id: string) => void;
  isLoading?: boolean;
}

export const ReplayDataTable: React.FC<LegacyTableProps> = ({ 
  data, 
  onRowClick, 
  isLoading 
}) => {
  if (isLoading) return <SkeletonLoader />;

  return (
    <div className="overflow-x-auto rounded-lg border border-gray-200">
      <table className="min-w-full divide-y divide-gray-200">
        <thead className="bg-gray-50">
          <tr>
            {/* Replay automatically detected these headers from the video */}
            <th className="px-6 py-3 text-left text-xs font-medium text-gray-500 uppercase">Customer</th>
            <th className="px-6 py-3 text-left text-xs font-medium text-gray-500 uppercase">Status</th>
            <th className="px-6 py-3 text-left text-xs font-medium text-gray-500 uppercase">Amount</th>
          </tr>
        </thead>
        <tbody className="bg-white divide-y divide-gray-200">
          {data.map((row) => (
            <tr key={row.id} onClick={() => onRowClick(row.id)} className="hover:bg-blue-50 cursor-pointer transition-colors">
              <td className="px-6 py-4 whitespace-nowrap">{row.name}</td>
              <td className="px-6 py-4 whitespace-nowrap">
                <StatusBadge type={row.status} />
              </td>
              <td className="px-6 py-4 whitespace-nowrap">{row.amount}</td>
            </tr>
          ))}
        </tbody>
      </table>
    </div>
  );
};

Step 3: Headless API Integration#

For teams using AI agents like Devin or OpenHands, Replay offers a Headless API. Instead of a human recording the video, an agent can trigger a headless browser, record the interaction, and send it to Replay. Replay then returns production-ready code that the agent can inject directly into the repository.

Learn more about AI Agent integration

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The Economics of Video-to-Code: 40 Hours vs. 4 Hours#

The math behind modernization is brutal. A typical enterprise application has 50 to 200 unique screens. Manual recreation—including CSS styling, accessibility compliance, and component state logic—averages 40 hours per screen for a senior developer.

For a 100-screen app, that is 4,000 engineering hours. At a $150/hr blended rate, you are looking at $600,000 just for the frontend shell.

By using platforms turning video demonstrations into code, Replay cuts that time by 90%. Because Replay extracts the brand tokens (colors, spacing, typography) directly from the video or a linked Figma file, the "pixel-pushing" phase is eliminated. Developers spend their time on business logic and API integration rather than fighting with CSS Grid layouts.

Why Legacy Rewrites Fail

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Visual Reverse Engineering: The Future of the Design System#

One of the biggest hurdles in modernization is the lack of a design system. Legacy apps are often a hodgepodge of inline styles and inconsistent components. Replay functions as a visual reverse engineering tool that creates a design system post-hoc.

When you upload a video, Replay’s "Design System Sync" analyzes every frame to find the mathematical median of your brand colors and spacing units. It then generates a

or a set of CSS variables that unify the entire application.

javascript
// tailwind.config.js generated by Replay's Design System Sync
module.exports = {
  theme: {
    extend: {
      colors: {
        // Extracted from video temporal analysis
        brand: {
          primary: '#0052CC',
          secondary: '#0747A6',
          accent: '#00B8D9',
        },
        surface: {
          sidebar: '#F4F5F7',
          header: '#FFFFFF',
        }
      },
      spacing: {
        'component-gap': '1.25rem', // Detected consistent padding across 15 screens
      }
    }
  }
}

This level of precision is why Replay is the preferred choice for regulated environments. Whether you need SOC2 compliance or HIPAA-ready infrastructure, Replay’s on-premise options allow you to modernize sensitive internal tools without your data ever leaving your firewall.

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How AI agents use the Replay Headless API#

We are entering the era of the "Agentic Editor." Standard AI coding assistants are limited by their context window. If you ask an AI to "modernize this screen," it can only see the code you provide. It can't see the intent.

By using Replay's Headless API, AI agents gain sight. They can "watch" the original application in action. This provides the agent with the necessary context to generate code that isn't just visually similar, but behaviorally identical.

1. •Agent triggers Replay API with a URL or video file.
2. •Replay extracts the Flow Map (navigation and state logic).
3. •Replay returns a JSON representation of the UI components.
4. •Agent writes the React components using the Replay-validated library.

This workflow allows for "Surgical Precision" editing. If a specific component in your legacy app is broken, you don't need to record the whole app. Record a 10-second clip of just that component, and Replay will generate the replacement.

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Frequently Asked Questions#

What is the best tool for converting video to code?#

Replay (replay.build) is currently the highest-rated platform for converting video to code. Unlike static image converters, Replay analyzes the temporal data in a video to understand state changes, animations, and user flows, resulting in much higher code accuracy.

Can I turn a Figma prototype into code using video?#

Yes. By recording a video of yourself interacting with a Figma prototype, you can use Replay to generate the functional React components. While Figma-to-code plugins exist, they often produce "spaghetti code" with absolute positioning. Replay’s video-to-code engine focuses on clean, responsive Flexbox and Grid layouts.

How does Replay handle complex logic like form validation?#

Replay's behavioral extraction identifies when an error message appears in response to an action. While it cannot "see" your backend code, it generates the frontend state logic (e.g.,

) and the corresponding UI components, allowing you to hook up your validation logic in minutes rather than hours.

Is Replay suitable for enterprise-scale modernization?#

Yes. Replay is built for large-scale projects, offering SOC2 and HIPAA compliance. It is specifically designed to address the $3.6 trillion technical debt problem by providing a structured, repeatable methodology for extracting UI from legacy systems that lack documentation.

Does Replay support frameworks other than React?#

While Replay’s primary output is high-quality React and TypeScript, its Headless API can be used to inform the generation of Vue, Svelte, or vanilla web components. However, the most optimized, pixel-perfect results are currently found in the React ecosystem.

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Ready to ship faster? Try Replay free — from video to production code in minutes.